Goof-Off
If it's latex paint, Goof-Off will probably get it out. You should test it on the fabric in an inconspicuous place.
Make sure you get Goof-Off and not Goo-Gone, which is something else. Goof-Off is naptha-based, I think. It also works really well on adhesive residue from stickers and tape, but you can't use it on plastics.
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